In this paper, we have reviewed the evidence suggesting that T-cell dysregulation is important in the pathogenesis of asthma. The history, clinical presentation, and an overview of the appropriate management of asthma have been briefly reviewed. T cells obtained from the airways of asthmatics display signs of activation; these changes mirror the intramural inflammation found at biopsy. There is debate about the importance of T helper/suppressor ratios in this population of cells, but alterations in these ratios have been noted with experimental allergen exposure, as well as during acute asthma attacks; some of these changes revert toward normal with steroid therapy. The division of T helper lymphocytes into Th1 and Th2 cells, first described in studies of murine immunology, appear to be relevant in humans, particularly in allergic disease. Although IL-4 and IL-5, prototypical Th2 cytokines, have been most clearly implicated in asthma, there is some evidence supporting a role for Th1 cells/cytokines as well.